In multifunction ophthalmic measurements, where each of the measurements has to be performed by a separate instrument, there arises the problem of how to mechanically arrange the instruments such that they can be simply switched from one to the other when changing the measurement to be performed. The optical axis of each measurement instrument must be accurately aligned with the eye to be measured, such that the problem in hand is not only the physical switching between one instrument and the other, but also the alignment of each instrument after it has been switched.
There exist a number of prior art documents which address this problem. For instance in U.S. Pat. No. 7,364,298, U.S. Pat. No. 7,515,321 and U.S. Pat. No. 7,771,050, all assigned to Nidek Co. Ltd., of Japan, there are described arrangements of ophthalmic apparatus capable of performing a plurality of eye characteristic measurements, using two separate measurement instruments stacked one on top of the other, which are moved in a vertical direction by a motion mechanism in order to switch measurements between them. Those patents relate to the combination of a tonometer for the measurement of intraocular pressure in a subject's eye using a unit blowing fluid onto the cornea through a nozzle, and an instrument for measuring the optical characteristics of the eye, in particular the eye's refractive power. In U.S. Pat. No. 7,909,462, assigned to Kabushiki Kaishi Topcon, there is described a similar combination instrument for tonometric and refractive characteristics measurements, in which the measurement heads are aligned side-by-side, and a method is described for switching between them by withdrawing them in a backward direction by a minimum distance, to enable the switch between them to be made in the minimum amount of time.
However, motion of complete measurement heads using linear motion stages can be a slow and mechanically complex technique. Furthermore, motion by means of a vertical lift when a lateral motion mechanism is also required to switch the measurement systems between the subject's left and right eyes may be equally complex. A simpler method of integrating two or more of such measurement modules into one instrument, which overcomes at least some of the disadvantages of prior art systems and methods, would therefore be advantageous.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.